NEW MATERIAL:The naphthacenequinone derivative of formula I (Hn is number of added hydrogen atoms when the double bond of the benzene ring is hydrogenated; n is 0 or 4).

EXAMPLE: 1,1-Dimethyl-1,2,3,4-tetrahydronaphthacene-6,11-dione of formula II.

USE: Digesting assistant for alkali pulp of lignocellulose or an alkylanthraquinone catalyst for the preparation of H2O2.

PROCESS: The compound of formula I wherein n is 4 can be prepared by cyclizing 2-(4-methyl-3-pentenyl)-1,4,4a,9a-tetrahydroanthraquinone in a polar solvent such as acetic acid in the presence of a strongly acidic catalyst such as p-toluenesulfonic acid. The product can be converted to another compound of formula I wherein n is 0 by oxidizing with molecular oxygen, usually air.